Pre-heat oven to 375 degrees.
In the bowl of an electric mixer or in a large bowl with a hand mixer or whisk, cream together butter and brown sugar until light and fluffy.
Add egg, lemon zest, and vanilla and mix until combined.
In a separate large bowl, whisk together flour, salt, and baking powder.
In batches, slowly begin adding the flour mixture into the wet mixture, until incorporated with the butter mixture, taking care not to over-mix. Gently fold in white chocolate chunks and blueberries.
Drop tablespoon balls of the dough onto an un-greased cookie sheet, making sure to leave about 1-inch between each cookie.
Bake for 11-13 minutes, until the edges have started to turn golden. Let in pan for a few minutes before moving to baking rack to cool completely.